CountDownLatch/CyclicBarrier/Semaphore使用过吗？(面试)

CountDownLatch：让一些线程阻塞直到另一些线程完成一系列操作后才被唤醒

CountDownLatch主要有两个方法，当一个或多个线程调用await()方法时，调用线程会被阻塞。其它线程调用countDown()方法会将计数器减1(调用countDown方法的线程不会阻塞)，当计数器的值变为零时，因调用await方法被阻塞的线程会被唤醒，继续执行。

//这个枚举一定要学会，项目中常用public enum CountryEnum{    ONE(1, "齐"),TWO(2, "楚"),THREE(3, "燕"),FOUR(4, "赵"),FIVE(5, "韩"),SIX(6, "魏");    @Getter private Integer retCode;    @Getter private String retMessage; countryEnum(Integer retCode, String retMessage){ this.retCode = retCode; this.retMessage = retMessage;    }    public static CountryEnum forEach_CountryEnum(int index){ CountryEnum[] myArray = CountryEnum.values(); for(CountryEnum element : myArray){     if(index == element.getRetCode()){  return element;     } } return null;    }}public class CountDownLatchDemo{    public static void main(String[] args) throws Exception{ CountDownLatch counDownLatch = new CountDownLatch(6); for(int i = 1; i  {  System.out.println(Thread.currentThread.getName()+"\t 国，被灭");  countDownLatch.countDown();     },CountryEnum.forEach_CountryEnum(i).getRetMessage()).start(); } countDownLatch.await(); System.out.println(Thread.currentThread.getName()+"\t 秦帝国，一统华夏"); System.out.println(CountryEnum.ONE); System.out.println(CountryEnum.ONE.getRetCode()); System.out.println(CountryEnum.ONE.getRetMessage());     } public static void closeDoor() throws InterruptedException{ CountDownLatch counDownLatch = new CountDownLatch(6); for(int i = 1; i  {  System.out.println(Thread.currentThread.getName()+"\t 上完自习，离开教室");  countDownLatch.countDown();     },String.valueOf(i)).start(); } countDownLatch.await(); System.out.println(Thread.currentThread.getName()+"\t 班长最后关门走人");    }}

CyclicBarrier：字面意思是可循环(Cyclic)使用的屏障(Barrier)。它要做的事情是，让一组线程到达一个屏障(也可以叫同步点)时被阻塞，直到最后一个线程到达屏障时，屏障才会开门，所有被屏障拦截的线程才会继续干活，线程进入屏障通过CyclicBarrier的await()方法

public class CyclicBarrierDemo{    public static void main(String[] args){ //CyclicBarrier(int parties, Runnable barrierAction) CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () -> {     System.out.println("召唤神龙"); }); for(int i = 1; i  {  System.out.println(Thread.currentThread().getName()+"\t 收集到第："+tempInt+"龙珠");  try{      cyclicBarrier.await();  }catch(InterrupttedException e){      e.printStackTrace();  }     },String.valueOf(i)).start(); }    }}

Semaphone：信号量主要用于两个目的，一个是用于多个共享资源的互斥使用，另一个用于并发线程数的控制

public class SemaphoreDemo{    public static void main(String[] args){ Semaphore semaphore = new Semaphore(3);//模拟3个停车位 for(int i = 1; i  {  try{      semaphore.acquire();      System.out.println(Thread.currentThread().getName()+"\t 抢到车位");      try{//暂停一会儿线程  TimeUnit.SECONDS.sleep(3);}catch(InterruptedException e){e.printStackTrace();}      System.out.println(Thread.currentThread().getName()+"\t 停车3秒后离开车位");  }catch(InterrupttedException e){      e.printStackTrace();  }finally{ }     },String.valueOf(i)).start(); }    }}